The present invention relates to improving a process for displacing oil by injecting a steam foam into (or forming it within) an oil-containing subterranean reservoir. More particularly, the invention relates to improving such a process by selecting the most effective one of a plurality of surfactant materials for forming a steam foam which is effective in both flowing preferentially into oil-containing portions of the reservoir and displacing that oil within the reservoir.
It is known that foams or foam-like mixtures of gas and liquid are less mobile within a permeable porous material, such as an earth formation, than are either the gaseous or liquid components of such a foam. Prior oil-displacing uses of foams are described in patents such as the following: U.S. Pat. No. 4,086,964 by R. E. Dilgren, G. J. Hirasaki, H. J. Hill and D. G. Whitten describes injecting steam, surfactant, noncondensible gas and electrolyte for forming a steam foam which is significantly less mobile than steam. U.S. Pat. No. 4,393,937 by R. E. Dilgren and K. B. Owens describes an improvement of the U.S. Pat. No. 4,086,964 patent using an alpha-olefin surfactant which is capable of reducing the mobility of the injected fluid to a greater extent than that provided by the most effective surfactant described in the prior patent. In those patents, as well as the Ser. No. 530,156 patent application, the criteria by which the surfactant to be used was judged amounted to comparing the permeability to steam of a sand pack containing the reservoir oil at residual oil saturation with the permeability to the steam mixed with the surfactant material.
Other prior processes for selecting the surfactant to be used in forming a foam amount to comparisons based on measurements of the height of foam the surfactant can form within an open column, comparing such foam heights before and after heating the surfactant, measuring the pressure gradient developed by surfactant-containing mixtures flowing through permeable porous media, such as sand packs, and the like. U.S. Pat. No. 3,357,487 measures the heat stability of a surfactant by measuring the surface tension of an aqueous solution of it before and after heating at 650.degree. F. for two hours. U.S. Pat. No. 4,148,217 compares the pressure drops during displacement of water with mixtures of water in the presence and absence of the surfactant to determining the foam forming strengths of surfactant which might be used in steam foam oil displacement processes. U.S. Pat. No. 4,458,759 suggests that, for improving the oil recovery from steam injected at about 365.degree. to 500.degree. F., almost any organic sulfonate surfactant is suitable as long as its decomposition rate at such temperatures shows "a leveling off trend after about 5-10 hours" (Col. 2, lines 59-64).